|
Roofing Systems...
Built-Up Roofing
Built-up roofing, sometimes referred to as ("tar and
gravel") was introduced during the 1840s and built-up roofing remains the
predominant system installed on low-slope ("flat") roofs.
A built-up roof system consists of multiple plies of reinforcing material
(organic felts, fiberglass mats or polyester), inter-ply layers of bitumen
(asphalt or coal tar) and a finish surfacing, such as gravel or decorative
rock, mineral surface cap sheets, or coatings. Owing to energy concerns,
many built-up systems today incorporate a rigid board insulation as well.
The repetitiveness of a built-up roofing system -- its layer upon layer
nature -- provides both flexibility and durability. The number of plies and
the materials used for surfacing can be varied to adapt the system to
virtually any environmental or aesthetic concerns. For the same reason, a
built-up roof is more forgiving of abuse after application than are many
other roofing systems.
top of page
Modified Bitumens
Modified Bitumens were developed in Europe during the
1960s and have been in use in the United States since the mid-1970s. The
idea was to improve upon the natural properties of bitumens by modifying
them during the manufacturing process. Typically, this means adding
either plastic or rubber.
When Atatic Polypropylene (APP) is blended into asphalt it makes it more
flexible and increases its resistance to ultraviolet radiation. Some APP
modified bitumen materials have granules embedded in the top surface for
further UV protection and to achieve a fire rating.
The other major modifier for bitumen is Styrene Butadiene Styrene (SBS),
a rubber-like material which improves the ability of sheets to elongate
and recover. SBS sheets are generally mopped down with hot asphalt or
cold adhesive, but some can be torch-applied. Unlike APP modifieds, SBS
is susceptible to damage from long-term exposure to ultraviolet
radiation, so surfacings are necessary to protect them.
Because they are so flexible, modified bitumens are commonly used as
flashing materials in built-up roofing systems.
top of page
Cold-Process Roofing
An alternative to traditional built-up
roofing, cold process roofing gets its name from the simple fact that hot
asphalt is not utilized. In place of hot asphalt, "cold" asphalt emulsions
or adhesives are applied between polyester mats or fiberglass base sheets.
A surfacing, typically a ceramic granule
surface or rock, is then usually applied over the membrane to provide
protection from ultraviolet radiation and to achieve a fire rating.
Today, many of the manufacturers of built-up
roof systems carry a product line and specifications designed for cold
process applications. It is a widely approved and acceptable roof system
found in today's architectural designs.
top of page
Single-Ply Roof Membranes
This class of low-slope roofing materials encompasses a variety of products
which share the common characteristic of being designed to be installed in a
single layer. Single ply materials are also highly flexible, which is why
they are sometimes referred to as "flexible membrane systems".
There are two main types of single ply product: thermosets such as EPDM,
CSPE and Neoprene are synthetic rubbers; thermoplastics such as PVC and EIP
are plastic-based materials.
Both types of membrane are highly flexible and resistant to ultraviolet
radiation. They are also comparatively easy to install. But they are also
generally incompatible with one another and cannot be used in combination on
a single roofing system.
top of page
Asphalt Shingles
Asphalt shingles are the most commonly used
and among the least expensive of materials available for steep slope
applications. They are very durable and are available in a wide variety of
colors and textures.
Asphalt shingles consist of either an organic (wood fiber or cellulose) or
fiberglass mat which has been saturated with asphalt and covered with
colored mineral granules. In climates where fungus growth is a potential
problem, granules treated with algecide are available. "Self-sealing"
shingles have an additional strip of adhesive on the underside. The adhesive
is activated by the sun's heat after installation and "seals" each shingle
to the one below it, providing extra wind uplift resistance for the roof
system.
Shingles were once available in only one thickness, but today many
manufacturers offer shingles where several layers have been laminated
together to produce three-dimensional profiles and appealing shadow lines.
These are known as "dimensional" or "architectural" shingles.
top of page
Tile Roof Systems
Clay tile and concrete tile offer comparable benefits to
slate, but with greater variety and at less cost. Tile is very durable and
fire resistant. It is available in numerous profiles, styles, finishes and
colors.
Tile is also less expensive that slate
(although it is also generally more expensive than asphalt shingles and
fiber-cement products). Like slate, however, tile is relatively heavy, and
its use may require roof reinforcement to support additional weight factors.
top of page
Shake, Wood and Shingle Simulations
Wood Shakes/Shingles Wood shakes and shingles
are made from cedar, cypress, redwood, southern yellow pine and other woods.
Shingles are sawn on both sides to a uniform thickness and an even taper.
Shakes are generally split on one or both surfaces for a more textured
effect, and they tend to be thicker at the butt end than shingles.
Fiber-Cement Roofing Materials products consist of cement and organic or
inorganic reinforcing fibers. They are designed to combine the look of
materials such as wood shakes/shingles, slate and tile with advantages such
as lower weight and higher fire ratings.
Historically, wood shakes and shingles have
been very popular in California. In recent years, however, their use has
declined because of concern about their fire resistance. U.L. classified
wood shakes and shingles which have been pressure-treated with fire
retardants are readily available, but some communities restrict or ban the
use of wood roofing materials, regardless of their fire rating.
top of page
| 
